A power converter such as an inverter, a servo amplifier, or a switching power supply incorporates therein one or a plurality of power semiconductor switching elements. The power semiconductor switching element undergoes a change in the conduction state between a first main terminal and a second main terminal in accordance with an electrical signal applied between a first signal input terminal and a second signal input terminal. A gate drive circuit receives a command signal from an upper controller to apply an electrical signal between the first signal input terminal and the second signal input terminal of the power semiconductor switching element and drive the power semiconductor switching element.
When the power semiconductor switching element is off, a current does not flow between the first main terminal and the second main terminal even with a high voltage applied therebetween. However, an excessively high voltage applied to the power semiconductor switching element causes a failure of the power semiconductor switching element. A technique has thus been proposed in which a voltage of each part of the power converter is detected and transmitted to the gate drive circuit. The gate drive circuit performs an operation that changes a method of driving the power semiconductor switching element on the basis of information on the transmitted voltage.
With the background art described above, Patent Literature 1 below presents a motor drive system for an electric vehicle. A voltage detection circuit is attached to a DC power supply in the motor drive system to detect a voltage. The voltage detection circuit transmits a signal to the gate drive circuit when the voltage of the DC power supply is higher than or equal to a predetermined voltage. Upon receiving the signal, the gate drive circuit changes the connection configuration of a gate resistor and changes the method of driving the power semiconductor switching element. The gate drive circuit prevents excessive generation of a surge voltage when the power semiconductor switching element is turned on and turned off. This prevents the application of an excessively high voltage to the power semiconductor switching element.
In Patent Literature 2 listed below, a first main terminal of a power semiconductor switching element and a gate drive circuit are connected by wiring. This wiring allows transmission of the voltage between the first main terminal and a second main terminal of the power semiconductor switching element to the gate drive circuit. The gate drive circuit detects the voltage between the first main terminal and the second main terminal of the power semiconductor switching element. The gate drive circuit changes the resistance value of a built-in resistor in accordance with the voltage between the first main terminal and the second main terminal to change the method of driving the power semiconductor switching element and prevent excessive generation of the surge voltage when the power semiconductor switching element is turned on and turned off. This prevents the application of an excessively high voltage to the power semiconductor switching element.